Adhesive connected joint assemblies are beginning to be more prevalent as the choice for assembling two structural elements together, whether or not the structure is a static or dynamic structure, such as is a structure used on an airplane. More importantly, the adhesively connected joint assembly provides a way by which structural components are bound together without requiring mechanical fasteners, especially when the material of each component of the joint is either a composite-to-composite or a composite-to-metallic type connection and would otherwise require excessive material waste to fashion a typical flange joint connection out of one of the parts capable of receiving mechanical fasteners. By utilizing the adhesively connected joint to connect structural elements, the weight of the overall structure may be reduced and the structural strength in a particular application may be increased.
One such adhesively connected joint is the pi-joint assembly used for aircraft structures which includes the PI structure, known for its shape resembling the mathematical π symbol. The pi-joint assembly includes a web, a pi member and a skin. An adhesive is then typically filled in the gap formed between the web and the pi-member in such a way as to secure the two members. Other pi members may be joined to the other sides of the web in order to complete a given structure, thereby allowing structures like a wing of an airplane to be formed by multiple pi-joint assemblies. Historically, aircraft structures were bent-up sheet metal with crude tolerance control bolted to supporting structures. This necessitated the use of assembly jigs for final location of the mating aircraft structure utilizing shims between the mating parts to accommodate the manufacturing tolerance inaccuracies. The adhesively connected joint or pi-joint is an improvement upon traditional aircraft structures. However, pi-joint has created a disadvantage by necessitating the need to use shims and other assembly jigs for final location and assembly of the joint. The flat panel or web location must be controlled within the pi-member to assure that an adequate adhesive bondline thickness is provided on all sides of the web inside the joint. If the web shifts to one side preventing adhesive from that surface, joint failure can occur. Another disadvantage of such joints is the complicated assembly procedures required in order to properly align the parts prior to applying the adhesive to secure the web to the pi-member.
One known process to assemble the parts is by utilizing holes located in the parts, whereby the parts are located and aligned during assembly. The holes are then drilled to size after the parts are assembled, which necessitates the requirement of subsequently disassembling the parts to remove drill lubricant, chips and other foreign matter introduced between the parts during the drilling process. The cleaned parts are then reassembled and fasteners or jigs are installed along the part to “hold” the parts in alignment with each other while the adhesive is injected into the parts and while it cures. The alignment process may include shims or wires that are positionally located along and between the parts in order to insure a bondline thickness. The minimum bondline thickness is required in order to insure maximum attachment strength between the adhesively joined parts. After the adhesive starts to set or has partially cured, the shims and wires are removed. The voids that are created by removal of the shims and wires are then filled with additional adhesive. The additional steps of locating, drilling, cleaning, reassembly, fastening, shimming, unfastening, unshimming, and filling voids as mentioned above are a disadvantage because time and money are lost due to the additional albeit necessary steps for the present method of assembly. Therefore, there is a need to have an improved method of assembly that reduces or eliminates the current steps. Also, there is a need to have an improved assembly that reduces or eliminates some of the assembly steps, assembly cycle time or assembly costs. Moreover, it would be advantageous to develop parts that reduces the dependency on tooling during the assembly process, reduces variation for part-to-part indexing and improves product repeatability and consistency. Lastly, it would be advantageous to eliminate the need for shims and/or wires to achieve the minimum bond thickness on a pi-joint and it would be advantageous to eliminate or reduce some of the associated assembly steps required by the shimming.
It may be beneficial to use Determinant Assembly (DA) technology in a novel and inventive way to solve or improve the uncertainty of locating and aligning pi-assembly members. It may also be beneficial to use DA technology features in order to provide an improved method of joint assembling. With the advent of close tolerance N/C machines, designers can now create accurately mated net-fit structures that can self locate on the mating parts. Features can be designed and built into the mating parts to assure prescribed locations. This practice is known as Determinant Assembly (DA) since the location of each detail is “determined” by features on the mating details of the assembly. Coupled with the increasing use of fastener-free bonded composite aircraft structural joints, there is an ever-increasing need to take advantage of the DA practice. This will provide increased accuracy of part locations, elimination of assembly jigs, and rapid production rates. Therefore it may be desirable to utilize DA technology, DA concepts and DA features on the parts in order to provide an improved adhesively bonded joint and method of assembling thereof.